From: guyren@... Date: 2016-06-27T06:17:10+00:00 Subject: [ruby-core:76156] [Ruby trunk Bug#12521] Syntax for retrieving argument without removing it from double-splat catch-all Issue #12521 has been updated by Guyren Howe. #12522 is a related issue; keyword arguments lvalues have a related issue. ---------------------------------------- Bug #12521: Syntax for retrieving argument without removing it from double-splat catch-all https://bugs.ruby-lang.org/issues/12521#change-59363 * Author: Guyren Howe * Status: Open * Priority: Normal * Assignee: * ruby -v: * Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN ---------------------------------------- There is an interesting style of programming that is *almost* really easy to do in Ruby. It would work elegantly with a simple change. A double-colon keyword argument should be available that will still leave the same argument captured by a double-splat argument if present. With this available, it becomes easy to pass down a "context" through a call chain. Consider this: ``` def controller name::, **context ��� log_then_render something:, name:, **context end def log_then_render **context log context complex_logic_then_render **context end def complex_logic_then_render name::, **context ��� Bunch of further calls def render name::, something::, **context ��� end ``` Now assume I decide render needs a foo argument, that I obtain in my controller. The only functions that are aware of or have any need for the argument are controller and render. With functions written in this style, I only need to modify the two functions that need to know about the argument: ``` def controller name::, **context ��� log_then_render something:, name:, foo: foo_value, **context end ��� no changes ��� def render name::, something::, foo:: **context ��� now use foo ��� end ``` This is, I accept, unusual. I've not seen a language that offers this sort of feature (I call them, for various reason I don't have time to go into now, FREST functions). I can basically implement this now with a decorator, but it's a little ugly and slow. It just occurred to me that an alternative would be a triple-splat final argument (or some such) that gathers all the keywords. There is a related problem with the way double-splat and regular keyword arguments interact that should be fixed anyway. -- https://bugs.ruby-lang.org/ Unsubscribe: